A cathode peel-off test process is conventionally known as a test process for examining an adhesion force of the coating film of such a test material (for example, see Japanese Patent Application Laid-open No.7-195612).
In this test process, a procedure is employed which involves immersing a test material having a damaged portion formed on the coating film to reach the metal blank, into an aqueous solution of NaCl serving as an electrolytic liquid, and allowing a DC current to flow between the metal blank serving as a cathode and an electrode provided in the aqueous solution of NaCl.
During supplying the electric current, OH ion produced by the electrolysis of water on the side of the metal blank as the cathode causes the adhesion force of the coating film to the metal blank to be decreased from a starting point provided by the damaged portion of the coating film, thereby promoting the peeling-off and blistering of the coating film. In this way, the cathode peel-off test process has an advantage that the superiority and inferiority of the adhesion force of the coating film can be simply determined. However, corrosion of the metal blank accompanying the peeling-off of the coating film cannot be predicted, and the cathode peel-off test process suffers from a problem that the overall estimation of the corrosion resistance cannot be carried out for the test material.
Therefore, a cycle corrosion test (CCT) is employed which is capable of simultaneously estimating the deterioration of the coating film and the corrosion of the metal blank.
However, the cycle corrosion test is accompanied by a problem that it requires a lot of test time and for this reason, a test result cannot be obtained early.